Preliminary Detailed Design
Team Vision for Preliminary Detailed Design PhaseThe goal of the Preliminary Detailed Design Phase was to create a detailed design plan for the project proof of concept. By the end of the phase, we completed the following:
- Feasibility Analysis of chosen design concepts
- Detailed drawing packages of the proof of concept
- Full Bill of Materials for proof of concept
- Detailed Systems Architecture
- High Level Software Flowchart
- Electrical Schematics for major electrical components such as micro-controller, motors, and entire ATLAS system
- Preliminary Test plans for key system components
- ATLAS Configuration Management Plan
Mechanical Design: Feasibility, Prototyping, Analysis, Simulation
We performed extensive research on various 3D printer
concept designs to better understand how to most
effectively model a Cartesian coordinate linear
positioning system. A design that we believe provides the
best guide to follow is that of the Prusa i3 Mk3 model. A
picture of the system can be found below.
We want to model the carriages of our system in the same fashion as the Prusa. The picture below shows an example of how the timing belts are hooked up to the carriage.
Although it provides the basic framework for our design, it will need to be heavily modified to meet our needs, such as adding a scalability aspect, a camera mount, etc. Another important modification is the movement in the vertical axis. The Prusa model utilizes a lead screw for this movement, which is very slow. This isn't an issue for a 3D printer but would be for our design. In order to meet our speed requirements, we needed to decide on a drive system for the vertical Y-axis. Including the lead screw used for the Y-axis and the timing belt used for the X-axis, we researched four different linear positioning systems shown in the table below.
With the level of accuracy and speed required for our system, we decided to further explore the ball screw drive and timing belt drive options.
Ball Screw Drive
BackgroundBall screw drives essentially consist of a screw and a nut. The screws are manufactured to a high precision grade and the nut is similar to a ball bearing system, where steel balls in the nut roll along the grooves of the screw. The screw is rotated by the motor and the nut travels based on the direction of rotation.
Design Parameters & CalculationsThe Ball screw system would have Fixed-Floating end supports. This means that one end would be rigid and fixed with double bearings to the motor and motor housing and the other end would be fixed to a single bearing and a supporting block connected to the MFD.
The following is a table of nominal parameters used that will fulfill the engineering requirements of our system:
The lead is a function of the desired speed of the system and the motor torque. Through the following calculation, the lead of the system would need to be 35.56 mm or larger.
The cost of implementing a ball screw drive would be between $500 and $1000 for the full-size range of the ATLAS Too system.
Timing Belt Drive
BackgroundThe timing belt drive system translates rotary motion into linear motion through a pulley. The pulley is directly attached to the motor and through a pulley at the opposite end of the system and to the carriage.
Design Parameters & CalculationsBased on the engineering requirements specific to our design, the specifications for the timing belt and pulleys were determined, as shown in the following table. The system will feature T5-pitch trapezoidal belts with widths of 15mm. Each belt will be secured to the component it is moving by being secured around knobs on the back of the component.
The cost of implementing the timing belt linear drive system would be about $100 across the full-size range of the ATLAS Too system.
We decided to proceed with the Timing Belt linear positioning drive largely due to cost.
ScalabilityTo simplify the scope of the design, we decided to create two size ranges for the final product. Our initial engineering requirement was to create a device that is compatible with MFDs as small as 6"x9" and as large as 30"x30". The two size ranges of the final product will be: Small to Medium and Medium to Large. The Small to Medium size range will cover MFDs as small as 6"x9" and as large as 14"x19". The Medium to Large size range will cover MFDs as small as 14"x19" and as large as 24"x30".
The mechanical drawings for the design can be found here:
Due to the tap speed requirement, an analysis was performed for the linear actuator from the previous ATLAS team and the linear actuator that we planned on purchasing.
From the Power Analysis Table, we need a Power Supply of at least 12V and 10A. We plan to do more research on a power supply next phase.
Additionally, we will be looking into using a second Raspberry Pi in order to break the system into modules.
Software FlowchartThe flow chart below represents the top level software design for the atlas and its subcomponents.
Configuration Management Plan
Bill of Materials (BOM)From the known design components, a Bill of Materials was created for the Proof of Concept.
The budget created in Phase II was also updated to reflect the purchases made so far.
The full Phase III updated budget worksheet can be found here.
Test Summary MatrixThe test summary matrix shows the relationship between the test plans and the risks that are associated with this project. The entire document can be found here.
The test plans are a complete document of criteria and procedure for testing critical requirements of the system. The example test plan is shown below. The entire document can be found here.
You can find the full document for the risk management strategies here.